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The purpose of our work was to compare the efficiency of two programs for the induction and synchronization of estrous and ovulation in acyclic cows (Ovsynch and Select Synch). To the first batch of 18 cows we have given 2ml Cystorelin (100 mcg GnRH) on day 0, on day 7th 2ml Estrumate (500 mcg of Cloprostenol, on the ninth day we administered 2ml Cystorelin (100 mcg GnRH), after 16 hours we conducted artificial insemination. To the second group of 14 cows we have given 2ml Cystorelin (100 mcg GnRH) on day 0, on day 7th we administered 2ml Estrumate (500 mcg of cloprostenol), heat detection was made at 24-48 hours after PGF2α and continued 5 to 7 days. Cows were inseminated at 8-12 hours after estrous detection. 60 days after the artificial insemination, 11 cows (44%) of the first group and 9 cows (41%) of the second batch were diagnosed as pregnant. These two protocols of inducing and synchronizing estrous are very effective in acyclic cows. [ABSTRACT FROM AUTHOR]

Administration of GnRH in the luteal phase of estrous in dairy cows induces an increase of LH levels, with the modification of the growth waves of the ovarian follicles. GnRH induces ovulation or atresia of the dominant follicle and the recruitment of a new wave of follicular growth. The GnRH administration in the luteal phase of the estrous cycle induces growth waves synchronization of ovarian follicles, so that, a new wave of follicles started to grow at 5-6 days after administration. In our experiments, we administered 2ml Ovarelin (100 mcg GnRH), to three groups of cows (116 cows): in early luteal phase of the estrous cycle (days 4-5), in the middle of luteal phase (days 9-12), and late luteal phase (days 15-16). The rates of cows standing heat were 91.66% when GnRH was administered in early luteal phase, 95.22% when was administrated in the middle of luteal phase, and 73.68% in late luteal phase GnRH administration. After artificial insemination, the conception rates were 48.48% in early luteal phase, 52.5% at middle luteal phase and 46.42% in the late luteal phase of the estrous cycle. [ABSTRACT FROM AUTHOR]

At dairy cows, the increase in milk production is associated with the decrease of heat manifestation and conception rates. GnRH is mostly used for treatment of different problems of the reproductive function and for improving the pregnancy rates in cows. The aim of our paper was to contribute to increase of conception rates, at cows with ovarian activity, at first AI after calving. The experiments were conducted on 58 cows, from Romanian Black Spotted breed (Frezian) and 53 cows from Romanian Spotted breed (Simmental). The animals were divided into lots as follows: for Romanian Black Spotted breed 33 of the cows in were in experimental lot and 25 were in control lot, for Romanian Spotted breed 29 ere in experimental lot and 24 were in control lot. The females form experimental lots were treated with 100 mcg (2ml) Ovarelin (GnRH), at the first AI, after VWP. At the cows form Romanian Black Spotted, from the 33 females in experimental lot, 12 did not return into heat after insemination, which represents a conception rate of 36.4%. At the cows form Romanian Spotted, form the 29 cows in experimental lot 8 did not return into heat after insemination, representing a conception rate of 44.8%. Administration of 100 mcg GnRH (2 ml Ovarelin) at the time of AI determines a significant increase of the conception rate with 8.4-11.5%, compared with control lot. It appears that the cows from Romanian Spotted reacts better at GnRH treatment (44.8% conception rate), compared with Romanian Black Spotted (36.4 % conception rate). [ABSTRACT FROM AUTHOR]